Electrosurgical instruments that use an electrical discharge taking place in a fluidic medium in order to act on biological tissue are known in principle. Such instruments for example include argon plasma coagulation instruments, which generate a spark burning in argon atmosphere or a plasma jet, or sparking scalpels or the like. Monopolar and bipolar resection instruments are known which, in non-conductive (Purisole) or conductive (saline solution) liquid, heat the liquid such that the liquid evaporates and sparks to the tissue or a further electrode form in this vapour. When handling argon plasma coagulation instruments, particular care must be taken when foreign bodies, in particular metal foreign bodies, are present in the biological tissue. These bodies may be, for example, stents or other metal parts, which have been implanted already in a patient in the past or which have been implanted during the current intervention. If the spark or plasma acts unintentionally on a stent, a metal clamp or another metal body in the biological tissue, this may cause damage to the metal part, whereby said metal part may lose its function. The surrounding tissue may also be damaged undesirably, for example on account of heat conduction.
On the other hand there are cases in which it is desirable for the spark or plasma to act on the metal foreign body, for example in order to shorten a stent or to perform certain surgical interventions. These include, for example, the coagulation of a bleeding vessel by means of anatomical tweezers, heated selectively by the spark or plasma jet of the electrosurgical instrument and thus capable of coagulating the vessel.
It is also known, for the application of monopolar and bipolar resection loops in the case of TUR, that too short a distance between the resection loop and the resectoscope unintentionally results in sparking onto the metal resectoscope. This undesirable sparking leads to a flow of current through the metal resectoscope. Since the resectoscope is in turn in contact with the biological tissue, this results in undesirable coagulation effects on the tissue.
An object is therefore to create a concept with which the action of a sparking electrical instrument on metal can be reliably differentiated from the action of the instrument on biological tissue.